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fested manure (C&EN, Dec. 11,2006, page 28). In the taco incident, as many as 150 people across the Northeast and upper Midwest became ill after eating at Taco Bell and Taco John's restaurants. At the height of the outbreak, about 90 restaurants across the Northeast and Midwest were closed. Many of the victims ended up in hospitals, and some are still relying on kidney dialysis to stay alive. After a long investigation, FDA decided that the cause was lettuce contaminated with the same microbe as was on the spinach—E. coli 0157^7. Ten years ago, the majority of foodrelated E. coli infections were caused by contaminated ground beef. But those incidents have declined 42% since 1996, when the Department of Agriculture established the Hazard Analysis Critical Control Points system for meat-processing plants. In recent years, E. coli 0157^7 infections have been linked mostly to fresh produce, primarily from central California. In all, 20 documented incidents involving leafy vegetables have occurred in the past decade. E. coli 0157:1^7 is a particularly nasty microbe. It produces a poison called Shiga toxin, and microbe levels as low as 50 cells per gram of food can sicken a child, says Aubrey Mendonca, a food science researcher at Iowa State University. "With other organisms, such as Salmonella, you need a few thousand microbes per gram," he says. Furthermore, there are many sources of E. coli 0157:1^7—cattle, deer, some wild birds, other wild animals. It doesn't cause disease in animals, and the contamination in any particular field can be spotty, he explains, making it difficult to detect. Those who advocate the use of irradiation to kill E. coli say it should be used as a last step in a careful protocol for growing, harvesting, and processing vegetables. William Marler, a leading Seattle-based attorney who represents victims of E. coli poisoning, wants Congress and FDA to consider COLORFUL ARRAY Agricultural Research Service scientists look at a variety of lettuces grown in California's Salinas Valley, which has been the source of several E. coli contamination incidents.
FOOD IRRADIATION Recent E. COL/ OUTBREAKS heighten interest in the technology BETTE HILEMAN, C&EN WASHINGTON
FOOD-BORNE INFECTIONS cause about 76 million cases of illness, 325,000 hospitalizations, and as many as 5,000 deaths in the U.S. annually. In other words, they send one in 1,000 Americans to the hospital each year and kill thousands. There is no single way to prevent all foodborne illness, but many food safety experts believe irradiation—subjecting the food to ionizing radiation—should be used much more widely as part of an overall program to enhance safety. Radiation for this purpose is provided by gamma rays from cobalt-60 or by electron beams from a linear accelerator. The radiation damages the DNA of disease-causing bacteria, such as Salmonella or Escherichia coli 0157^7, as well as the DNA of insects, preventing reproduction. Gamma rays and electron beams have identical effects on food. But gamma rays penetrate farther than electrons, so they can be used to irradiate bulk foods in shipping pallets. About 50% of Americans hold negative opinions about food irradiation. They believe it is expensive and possibly dangerous and that it changes the flavor of the food. They also complain that it would lead to poor sanitary practices in the growing, harvesting, and processing of food. In the U.S., irradiation is employed primarily on spices, chicken, and ground
beef. The Food & Drug Administration has not yet approved it for pathogen control in fresh fruits and vegetables. In 1999, the Food Irradiation Coalition—a group of food processors, health organizations, and academic groups—submitted a petition to FDA to use irradiation on bagged fresh fruits and vegetables to help eliminate microbial pathogens, but the agency has not yet reached a decision. LAST YEAR'S outbreaks of E. coli 0157^7 in fresh bagged spinach and in lettuce served at Taco Bell and Taco John's restaurants, however, have increased interest in the technology. In the spinach incident in August and September, 204 people were sickened, 102 were hospitalized, 31 developed kidney failure, and three eventually died from eating contaminated spinach. The immediate cause of the spinach incident was feral pigs that ate grubs in cow manure on a free-range pasture and then wandered into neighboring spinach fields, contaminating the spinach with their in-
"Washing by itself won't take care of the problems because E. coli sometimes gets inside the cells of the produce." WWW.CEN-0NLINE.ORG
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Irradiation Has Benefits But May Hurt Flavor Other than spices and seasonings, ground beef and poultry are the primary foods irradiated in the U.S. The process clearly reduces pathogen levels in the products, but there is evidence that the treatment may degrade the flavor. Irradiation was approved for spices in 1983 and for insect control on fruits and vegetables in 1986, but it was not approved for use on poultry until 1992 and on red meat until 1997 All irradiated products sold in stores or delivered to homes must display a "radura" symbol and the words "treated with irradiation" or "treated by irradiation" on the label. According to Department of Agriculture rules, irradiation can be used on meat and poultry only after the food has met all food safety regulations and been inspected and passed by USDA. The department points out that the application of radiation, steam pasteurization, or any other pathogen-reduction strategy "does not mean the department will abandon or lessen its strict sanitation requirements or zero tolerance for fecal-matter contamination." Currently, in the U.S., all the frozen ground beef sold by the high-end distributors Omaha Steaks and Schwan Food Co. is irradiated. In addition, thousands of supermarkets, including those owned by Wegmans and Publix, offer fresh irradi-
ated ground beef. Only about 15 million lb of irradiated ground beef is sold annually, less than 1 % of the total, says Ronald F. Eustice, executive director of the Minnesota Beef Council. Wegmans successfully launched sales of irradiated ground beef in 2002 after it provided cooked samples in all stores for several weeks to allow customers the opportunity to taste the product before purchasing. In 2003, Consumer Reports magazine, published by Consumers Union, conducted the largest study to date of irradiated products offered in supermarkets, purchasing 500 packages of both standard and irradiated chicken tenders and ground beef in 60 cities. It found that the irradiated products had lower pathogen levels than conventional foods but still contained measurable levels. And in blind taste tests, "trained testers noted a slight but distinct off taste and smell like singed hair in most of the irradiated beef and chicken that was cooked and sampled," but "because the off tastes are usually subtle, some consumers may not notice," Consumer Reports noted. The magazine concluded that there is no reason to buy irradiated meat or poultry if "you cook meat thoroughly." It said the way irradiation is being promoted gives consumers a false sense
of security and may take the focus off preventing contamination in the first place. Consumers Union is opposed to end-of-pipe solutions. "Unlike systems that look at every critical control point, endof-pipe solutions foster carelessness early on in the growing and production process," Jean Halloran, director of the Consumer Policy Institute, a division of Consumers Union, explains. "Then, if the final step fails for any reason, you can have a very serious problem." The flavor changes in meat resulting from irradiation are caused by oxidation of lipids, says Aubrey Mendonca, a food science researcher at Iowa State University. Irradiation turns some of the water in the meat into free radicals that oxidize lipids, creating off tastes, he explains. "But if you freeze the meat before it is irradiated, you don't get a lot of these chemical changes," he says. The best approach is to use good sanitation, freeze the meat, and then irradiate it with the lowest effective dose, he observes. Robert V. Tauxe, a medical officer at the Centers for Disease Control & Prevention, estimates that irradiating half of all ground beef, pork, poultry, and processed meat would prevent 900,000 cases of food-borne illness and 350 deaths in the U.S. each year (Emerg. Infect. Dis. 2001, 7, 516).
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whether irradiation of "all mass-produced foods, including produce, is an option." To be successful, however, irradiation of fresh produce must be done very carefully, says Lane Highbarger, consumer safety officer at FDA's Center for Food Safety & Applied Nutrition. Because produce has a high water content, it tends to react poorly to intense radiation, he says. If the dose is too high, it changes the taste, texture, or odor of the food, he explains. "SOME STUDIES have been done on shredded leafy green vegetables to see what levels of radiation would be potentially effective at controlling microbiological contamination while keeping the quality of the food acceptable," he observes. "Leafy green vegetables irradiated at levels up to l kiloGray [kGy] have been shown to be indistinguishable from normal unexposed leafy green vegetables." For example, Xuetong Fan, research technologist at USDA's Agricultural Research Service, has found that most fresh-cut fruits and vegetables can tolerate 0.5 to 1.0 kGy radiation without significant deterioration in product quality. "However, 1 kGy often has only a moderate effect on controlling microbiological contamination," Highbarger says. But there are exceptions. Several researchers at Chapman, Iowa State, and Texas A&M Universities have come up with promising results with electron-beam irradiation. For example, Denise M. Foley, assistant professor of biology at Chapman, found that E. coli levels could be reduced by a factor greater than 100,000—a 99.999% reduction—if lettuce is first washed in a chlorine solution and then irradiated with a dose somewhat lower than 1 kGy. Alejandro Castillo, associate professor in the department of animal science at Texas A&M, inoculated spinach with three strains of E. coli 0157^7 and reduced the contamination to an undetectable level (below 10 cells per g of food) with an energy dose of 1.2 kGy The appearance of the spinach leaves was unchanged by the irradiation and the shelf life may have been improved, he says. Irradiation may be a viable alternative for decontamination of spinach, he explains, "but it should not substitute for good agricultural practices and sanitary processing." Jaejoon Han, a Texas A&M researcher, packed romaine lettuce in plastic bags coated with a natural antimicrobial agent and then subjected them to electron beam irradiation. The bags were coated with a plant-derived fnuzs-cinnamaldehyde
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product quality is probably necessary before FDA will act on the petition to irradiate bagged fresh vegetables and fruits. If it does eventually approve the petition, the agency will face strong opposition from many environmental and consumer groups who are fiercely opposed to the technology. Even though irradiating food with gamma rays or electron beams creates no radioactive components, the public-interest and consumer groups that advocate the creation of a single food safety agency and stronger regulations to protect food tend to oppose both nuclear power and food irradiation. It would take many more tragic foodpoisoning incidents and extensive public education before coalitions would emerge that would favor both stronger rules and laws to promote food safety and exposing foods to gamma rays or electron beams. Congress would have trouble taking any action on irradiation so long as public opinion remains extremely polarized. •
SAFETY STUDIES
USDA researchers vacuum-seal hot dogs to get them ready for irradiation
(traws-3-phenyl-2-propenal), which FDA considers safe for food use. He found that irradiation treatment combined with the antimicrobial packaging reduced the microbes 25% more than irradiation alone. "We should irradiate all fresh produce to eliminate microbial problems before they reach the consumer," says Elena CastellPerez, associate professor of biological and agricultural engineering at Texas A&M. "We are working on it here, trying to develop the right treatments so we don't reduce the quality of the produce," she notes. "Washing by itself won't take care of the problems because E. coli sometimes gets inside the cells of the produce. "OUR RESEARCHERS are getting data showing what doses would be appropriate for E. coli or Listeria in bagged leafy greens and mangoes," Castell-Perez explains. "We are working between 1 and 3 kGy. Maybe 1.5 kGy will do the j ob, but we need to look at whether it affects the quality of the produce. If we coat the plastic bags with an antimicrobial compound, maybe we can use only 1 kGy." The aim is to reduce the level of microbes by a factor of 100,000, she says. Castell-Perez believes that if produce is irradiated, no less care will be taken to see that it is grown and processed under sanitary conditions. She estimates irradiation would cost 5 to 10 cents per lb if done on a large scale. However, Tony Corbo, a lobbyist at Food & Water Watch, does not favor irradiation, even if it turns out to be inexpensive and the quality of the fruits and vegetables is preserved. He views irradiation as a BandAid when what is needed is a total overhaul of the food production system. "There is a growing amount of pollution that is impacting the entire food supply,
and somebody is going to have to come to grips with this," Corbo says. Dairy operations should not be situated near produce fields, and run-off from livestock should not be allowed in produce fields, he continues. "We should not resort to invasive technologies like irradiation to make up for the fact that we are producing food in a degraded environment." Robert V. Tauxe, a medical officer at the Centers for Disease Control & Prevention, says that current U.S. attitudes toward irradiation are very much like American's views of milk pasteurization in the 1930s before it became common practice. At that time, he explains, many people said pasteurization would be too expensive, reduce the vitamin content of the milk, and lead to unsanitary practices on dairy farms because pasteurization would be used as a final step to kill microbes. But in fact, widespread pasteurization adds little to the cost of milk and has eliminated many illnesses caused by pathogens in dairy products. More research to establish effective radiation doses that do not harm WWW.CEN-0NLINE.ORG
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